Introduction
Theenergyofoceancurrentisproportionaltothesquareofthevelocityandtheflow.Comparedwithwaves,oceancurrentenergychangesmoresmoothlyandmoreregularly.Thetidecanchangeitssizeanddirectiontwiceadaywiththeriseandfallofthetide.Generallyspeaking,theoceancurrentenergyofawaterwaywithamaximumvelocityof2m/sormorehaspracticaldevelopmentvalue.
Theso-calledoceancurrentmainlyreferstotherelativelystableflowinthesubmarinewaterwaysandstraitsandtheregularseawaterflowcausedbythetide.Oneofthemisseawatercirculation,whichreferstoalargeamountofseawaterflowingfromoneseaareatoanotherseaareaoveralongdistance.
Causingfactors
Thisseawatercirculationisusuallycausedbytwofactors:First,theseasurfaceisblowingwithconstantwindalltheyearround,suchastheconstantsoutheastonthesouthsideoftheequator.Thewind,anditsnorthsideistheconstantnortheasterlywind.Thewindblowstheseawatertomakethesurfaceofthewatermove,andthemovementofthewatertransmitsthismovementtothedepthsofthesea.Asthedepthincreases,theseawaterflowratedecreases;sometimesthedirectionofflowwillgraduallychangewiththeincreaseofdepth,andeventheflowdirectionofthelowerseawaterisoppositetothatofthesurfaceseawater.InthenorthernandsouthernhalvesofthePacificandAtlantic,andthesouthernhalfoftheIndianOcean,thedominantwindsystemcreatesavast,counterclockwiseoceancirculation.Inlow-andmid-latitudewaters,windisthemaindrivingforceforoceancurrents.Secondly,thetemperatureandsalinityofseawaterindifferentseaareasareoftendifferent,andtheywillaffectthedensityoftheseawater.Thehighertheseawatertemperatureandthelowerthesaltcontent,thelessdensetheseawater.Thedifferenceinseadensitybetweenthetwoadjacentseaareascanalsocauseseawatercirculation.Theflowofseawatergeneratestremendousenergy.Itisestimatedthattheglobaloceancurrentcanreachupto5TW.Thetidecanchangeitssizeanddirectiontwiceadaywiththeriseandfallofthetide.
Causesofoceancurrents
Theseaisfullofwater,whyareoceancurrentsformed?Thereareroughlythreereasonsfortheformationofoceancurrents.Themostimportantreasoniswind.Theprevailingwindblowstheseasurface,pushingtheseawatertomovewiththewind,andcausingtheupperseawatertodrivethelowerseawatertoflow.ThecurrentformedinthiswayiscalledForwindcurrentsordrifting.However,thisoceancurrentwillaccelerateandweakenasthedepthoftheseaincreases,untilitissosmallthatitcanbeignored.
Thesecondtypeofoceancurrentistheflowofseawatercausedbythedifferenceinseawatertemperatureandsalinityindifferentseaareas.Suchoceancurrentsarecalleddensitycurrents.Forexample,intheStraitofGibraltar,thesalinityoftheMediterraneanishigherthanthatoftheAtlantic,soatadepthof500m,theseafromtheMediterraneanflowstotheAtlanticthroughtheStraitofGibraltar,whileatthesurfaceoftheocean,theseafromtheAtlanticrushestotheMediterranean,supplementingthelackofMediterraneanseawater.
Othercausesofoceancurrentsincludegeostrophicflow,compensationflow,rivereffusion,riftflow,downstreamflow,etc.
Utilizationmethod
Powergeneration
Theutilizationmethodofoceancurrentenergyismainlypowergeneration.Itsprincipleissimilartowindpowergeneration.AlmostanyWindpowergenerationdevicescanbetransformedintooceancurrentpowergenerationdevices.However,sincethedensityofseawaterisabout1,000timesthatofairandmustbeplacedunderwater,oceancurrentpowergenerationhasaseriesofkeytechnicalproblems,includinginstallationandmaintenance,powertransmission,anti-corrosion,loadandsafetyperformanceinthemarineenvironment,etc.Inaddition,thefixedformandturbinedesignofoceancurrentpowergenerationdevicesandwindpowergenerationdevicesarealsoverydifferent.Theoceancurrentdevicecanbeinstalledandfixedontheseabedoronthebottomofthefloatingbody,andthefloatingbodyisfixedontheseabyananchorchain.Turbinedesigninoceancurrentsisalsoakeytechnology.
Assistingnavigation
Thetraditionaluseofoceancurrentsbyhumanbeingsisto"pushtheboatalongtheriver."Theancientsusedoceancurrentstodrift.Intheageofsailing,
Usingoceancurrentstoaidnavigationisjustaspeopleoftensay"pushtheboatalongthewater."Inthe18thcentury,AmericanpoliticianandscientistFranklindrewamapoftheGulfStream.ThemapspecificallymarkstheflowdirectionoftheNorthAtlanticoceancurrentindetail,andisusedbysailingshipstoandfromNorthAmericaandWesternEurope,greatlyshorteningthetimetocrosstheNorthAtlantic.IntheEast,accordingtolegend,duringWorldWarII,theJapaneseusedtheKuroshioCurrenttosendfoodtothemainlandonraftsfromChinaandNorthKorea.Modernsatelliteremotesensingtechnologycanmeasureoceancurrentdatainvariousseaareasatanytime,andprovidethebestroutenavigationservicesforshipsontheocean.
Theoceancurrentpowergenerationisalsovaluedbymanycountries.In1973,theUnitedStatestestedagiantoceancurrentpowergenerationdevicecalled"Coriolis".Thedeviceisapipelinetypehydroelectricgenerator.Theunitis110meterslong,withapipeopeningof170metersindiameter,andisinstalled30metersbelowtheseasurface.Undertheconditionofanoceancurrentflowrateof2.3meterspersecond,thedeviceobtains83,000kilowattsofpower.JapanandCanadaarealsovigorouslyresearchingandtestingoceancurrentpowergenerationtechnology.Inmycountry'soceancurrentpowergenerationresearch,prototypeshavealsoenteredtheintermediateteststage.
Theoceancurrentpowergenerationtechnology,exceptfortheabove-mentionedwaterwheelssimilartotheriverpowerstationpipelinediversion.Therearealsomechanicaldeviceslikewindmillbladesoranemometersoutsidethemachine.Akindofoceancurrentpowerstation.Therearemanyrunnersinstalledinseriesbetweentwofixedfloatingbodies,whichareopenedinasemi-circularshapeundertheimpactofoceancurrent.Itiscalledagarlandoceancurrentpowerstation.Inaddition,theaforementionedhydroturbinetidalcurrentpowergenerationshipcanalsobeusedforoceancurrentpowergeneration.
Powergenerationdevices
Oceancurrentpowergenerationdevicesmainlyincludevanetype,parachutetypeandmagneticcurrenttype.Thevane-typeoceancurrentpowergenerationdeviceusesoceancurrenttopushtheblades,andthebladesdrivethegeneratortogeneratecurrent.Thevanescanbeeitherpropellertypeorrunnertype.Theparachute-typeoceancurrentpowergenerationdeviceiscomposedofdozensof"parachutes"connectedinseriesonanendlesshingedrope.The"parachute"inthedirectionoftheseacurrentisopenedbytheforceoftheseacurrent,andtheparachuteinthedirectionoftheseacurrentisclosedbytheforceoftheseacurrent.The"parachute"opensandclosesinsequenceandreciprocates,drivingthehingeropeandthendrivingthehingeplateontheshiptorotate,andthehingeplatedrivesthepowergeneration.Machinepowergeneration.Themagneticcurrentoceancurrentpowergenerationdeviceusesseawaterastheworkingmedium,allowingseawaterwithalargenumberofionstopassthroughastrongmagneticfieldverticallytoobtaincurrent.Thedevelopmenthistoryofoceancurrentpowergenerationisnotlong,andthepowergenerationdeviceisstillinthestageofprincipleresearchandsmall-scaletesting.
Observationandanalysis
Thetheoreticalestimateofoceancurrentenergyintheworldisabout10^8kW.Usingvariousobservationsandanalysisdataof130waterwaysandnavigationgatesalongthecoastofChina,thetheoreticalvalueoftheannualaveragepowerofChina'scoastaloceancurrentenergyisabout1.4×10^7kWbycalculationandstatistics.Amongthem,theoceancurrentsalongthecoastofLiaoning,Shandong,Zhejiang,Fujian,andTaiwanarerelativelyrichinenergy.Manywaterwayshaveanenergydensityof15-30kW/m2,whichhasgooddevelopmentvalue.ItisworthpointingoutthatChina’soceancurrentenergyisoneoftheregionswiththehighestpowerdensityintheworld,especiallytheJintang,GuishanandXihoumenwaterwaysinZhoushanIslands,Zhejiang.Theaveragepowerdensityisabove20kW/m2,andthedevelopmentenvironmentisTheconditionsareverygood.
Relatedintroduction
CurrentsituationinChina
China'sseaareaisvast,withwindcurrentsanddensitycurrents;coastalcurrentsanddeep-seacurrents.Thevelocityoftheseoceancurrentsismostly0.5nauticalmileperhour,theflowratedoesnotchangemuch,andtheflowdirectionisrelativelystable.Ifcalculatedatanaverageflowof100cubicmeterspersecond,theenergyofChina’soffshoreandcoastalcurrentscanreachmorethan100millionkilowatts.Amongthem,theTaiwanStraitandtheSouthChinaSeahavethemostabundantenergy.Theywillprovidesufficientandcheapenergyforthedevelopmentofindustriesinmycountry’scoastalareas.Electricity.
Usingoceancurrentstogenerateelectricityismuchmoresuperiorthanriversonland.Itisneitherthreatenedbyfloodsnoraffectedbydryseasons.Itflowsalmostataconstantwatervolumeandacertainflowratethroughouttheyear.Itcanbeareliableenergysourceformankind.
Oceancurrentpowergenerationreliesontheimpactoftheoceancurrenttomaketheturbinerotate,andthentransformittoahighspeedtodrivethegeneratortogenerateelectricity.Oceancurrentpowerstationsaremostlyfloatingonthesea.Forexample,akindofoceancurrentpowerstationcalledthe‘garland’iscomposedofaseriesofpropellers,bothendsofwhicharefixedonapontoonwithageneratorinstalledinit.Theentirepowerstationfloatsontheseainthedirectionofthecurrent,likeawreathdedicatedtoguests.Thereasonwhythiskindofpowerstationiscomposedofaseriesofpropellersismainlybecausetheflowvelocityoftheoceancurrentissmallandtheenergyperunitvolumeissmall.Itspowergenerationcapacityisusuallyrelativelysmall,andgenerallycanonlyprovideelectricityforlighthousesandlightboats,atmostitcanonlychargethebatteriesonthesubmarine.
Technologicalinnovation
TheUnitedStatesoncedesignedabarge-typeoceancurrentpowerstationwhosepowergenerationcapacityismuchgreaterthanthatofarosette-typepowerstation.Thiskindofpowerstationisactuallyaship,soitseemsmoreappropriatetocallitapowership.Hugewaterwheelsareinstalledonbothsidesoftheship'sgunwale,whichcontinuouslyrotateunderthepushofoceancurrentstodrivegeneratorstogenerateelectricity.Thegeneratedelectricityissentashoreviasubmarinecables.Thiskindofbarge-typepowerstationhasapowergenerationcapacityofabout50,000kilowatts,andbecausethepowerstationisbuiltonaship,itcansailtoanearbyporttoescapewhenthereisastrongwindandwavestoensurethesafetyofthepowergenerationequipment.
Inthelate1970s,foreigncountriesdevelopedanumbrella-typeoceancurrentpowerstationwithanoveldesign,whichwasalsobuiltonaship.Itisastringof50parachutesonalongropetogathertheenergyoftheoceancurrent.Thetwoendsoftheropeareconnectedtoformaring.Then,puttheropeonthetwowheelsanchoredinthesternofthecurrent.Theparachuteplacedintheoceancurrentispropelledbythestrongoceancurrent,andtheparachuteinthecountercurrentislikeastrongwindthatexpandsandexpandstheumbrella,movingalongthedirectionoftheoceancurrent.Theparachute'sropethendrivesthetwowheelsontheship,andthegeneratorconnectedtothewheelsalsorotatestogenerateelectricity,andtheelectricityitemitsistransmittedtotheshorethroughthecable.